The most remarkable shield volcanoes in the world are the Hawaiian Islands. The 8 main Hawaiian Islands are made up of 15 shield volcanoes. The largest of these volcanoes is Mauna Loa. Mauna Loa is also the largest active volcano in the world. It is 30 miles (48.3 kilometers) wide and 60 miles (96.5 kilometers) long and makes up half of the Big Island of Hawaii. In contrast to its massive horizontal size, the mountain is only about 9 kilometers high from the seafloor. The Galapagos Islands are another famous chain of shield volcanoes. The main island in the chain, Isabela Island, is composed of merged shield volcanoes. Since Charles Darwin's first visit to the islands in 1835, scientists have recorded more than 60 eruptions at 6 volcanoes. Another distinctive feature of shield volcanoes is the frequent formation of calderas at their summits. Calderas form when volcanoes empty magma chambers near their surface. The surface above the caldera may collapse into the empty magma chamber, resulting in a bowl-shaped depression. The two best-known shields of the Hawaiian Islands, Kilauea and Mauna Loa, both have a summit